Split `angular.json` into multiple files

# 🚀 Feature request

- [x] new
- [x] build
- [x] serve
- [x] test
- [x] e2e
- [x] generate
- [ ] add
- [ ] update
- [x] lint
- [ ] extract-i18n
- [x] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

### Description

I have a monorepository and I want to split my `angular.json` into separate files.

So that I can have something like this:

```
{
"version": 2,
"projects": {
"module-auth": "packages/auth",
"module-core": "packages/core",
"module-button": "packages/button"
}
}
```

After working with NX I noticed that with Lerna and the usual setup my `angular.json` file has 119 lines of code even though I basically have an empty repository. I believe that having a single `angular.json` file is a very bad idea, especially for bigger monorepositories or UI libraries.

### Describe the solution you'd like

Make the JSON configuration 1:1 with [what NX does](https://nx.dev/configuration/projectjson#workspace-json) or implement similar functionality.

既存の angular.json 構造と、関連するものとしてマークされた Angular CLI コマンド（new、build、serve、test、e2e、generate、lint、run）から始めます。これらのコマンドが workspace 設定をどのように利用するかを追跡し、要求された NX-style レイアウトに一致する動作で、個別のプロジェクトファイルをサポートする方法を定義します。

索引モデルが issue の本文から書いたものです。